“Based on information provided to the Committee by individuals with direct knowledge of events in Libya, the attack that claimed the ambassador’s life was the latest in a long line of attacks on Western diplomats and officials in Libya in the months leading up to September 11, 2012,” Issa and Chaffetz wrote. “It was clearly never, as Administration officials once insisted, the result of a popular protest."

The congressmen said the consulate asked for more security to deal with the growing threat but was turned down by the administration.

“In addition, multiple U.S. federal government officials have confirmed to the Committee that, prior to the September 11 attack, the U.S. mission in Libya made repeated requests for increased security in Benghazi. The mission in Libya, however, was denied these resources by officials in Washington.”

The two lawmakers told Clinton they intend to convene a hearing of Issa’s House Oversight panel on Oct. 10 to review possible security failures in Libya, including “State Department security assessments and security related decision making.”

Clinton will “cooperate fully” with the Republican probe, the State Department said.

“The secretary intends to respond to the congressmen today,” State Department spokeswoman Victoria Nuland said at her daily briefing Tuesday.

“And her letter will make absolutely clear the desire of this department, her personal desire to cooperate closely with the committee and with all members of Congress, both in their document requests, in their requests for witnesses for their hearing, because we share the same goal: We want to get to the bottom of precisely what happened and learn any lessons that we need to learn from it. We're taking this very, very seriously.”

The letter from the GOP congressmen for the first time reveals an April 6 attack against the consulate in which two former security guards threw homemade improvised explosives over the fence of the compound.

The letter also says militants made no secret of their intention to target Americans in Libya.

On May 22, a warning message was posted on Facebook that a rocket-propelled grenade attack against the Red Cross offices in Benghazi would be followed by a “message for the Americans disturbing the skies over Derna.” A separate threat was made the following month against Ambassador Christopher Stevens that mentioned his morning run with a security detail, complete with a photo of the late ambassador.

Stevens and three other Americans were killed in a Sept. 11 attack on the consulate. The Obama administration initially blamed the attack on militants who acted spontaneously and used protests against an anti-Islam video posted online as cover.

But the administration has shifted its account, with Director of National Intelligence James Clapper calling it a “deliberate and organized terrorist attack” on Friday.